Automatic steering system



March 18, 1952 M. MaCCALLUM 2,589,834

AUTOMATIC STEERING SYSTEM Filed Jan. 31, 1946 E Q O 2 SHEETSSHEET l TTORNEY March 1952 A. M. M CALLUM 2,589,834

AUTOMATIC STEERING SYSTEM 1 Filed Jan. 51, 1946 2 SHEETS--SHEET 2 Patented Mar. 18, 1952 AUTOMATIC STEERING SYSTEM Alan M. MacCallum, Ma

ywood, N. J., assignor to Bendix Aviation Corporation, Teterbcro, N. J.

a corporation of Delaware Application .l'anuary 31, 1946, Serial No. 644,642

13 Claims. 1

The present invention relates generally to automatic steerin systems adapted for use with mobile craft and more particularly to systems which may be applied equally as well to the automatic steering of both air or water craft.

All electric automatic pilot systems heretofore known of the character shown and described in copending application Serial No. 516,488, filed December 31, 1943, are admirably suited for use with large craft such as, forexample, passenger or cargo craft, bombers, etc., but are not suitable for use with light, fast aircraft such as, military fighter craft, for example, and the present invention contemplates the provision of a lightweight automatic steering system for use with small and fast aircraft.

In providing automatic steering systems for mobile craft it is desirable that the system be so designed that the directional signal reference means he maintained in synchronism with the control surface during manual flight so that upon the initiation of automatic steering the entire system is in condition to take over control immediately without injecting severe jolts, etc., to the craft. In the aforementioned application one manner of attaining the desired end is illustrated by the provision of an inductive transmitter device within the master direction indicator which, during turn or manual flight, is centralized at its null position by means of centralizing .7

means so that upon the initiation of automatic steering the inductive transmitter device and the rudder will start from a null or neutral position. the inductive transmitter device being displaced during craft deviation from a prescribed course by a motor which also drives an inductive coupling device to its null position.

The novel automatic steering system of the present invention embodies a novel and more simple synchronizing expedient in that the inductive transmitter device is eliminated and, during turn or manual flight, a motor is free to drive an inductive coupling device to null so that the directional reference will always be in synchronism with the rudder control surface. During automatic flight, on the other hand, the motor is locked so that a signal will be developed in the inductive coupling device and retained there for communication to the rudder servomotor for the energization thereof for the return of the craft to its prescribed course.

An object of the present invention, therefore, is to provide a novel, simple and lightweight autoinatic pilot system adapted for providing one, two' or' three ares of control for air or water craft.

Another object of the invention is to provide a novel automatic pilot for use with fast and lightweight craft.

A further object is to provide a novel light weight automatic pilot having simple and novel synchronizing means therein whereby the steering system is always maintained in condition to immediately take over steering control from the human pilot.

Another object is to provide a novel automatic pilot in which rudder control is responsive to the algebraic sum of displacement, rate of displacement, and follow-up signals, the generating means for developing such signals being connected with each other in series.

A still further object of the invention is to provide a novel all electric automatic pilot for aircraft adapted for providing control about three axes of the craft and having automatic turn and trim provisions therefor.

The above and other objects and advantages of the present invention will appear more fully hereinafter from a consideration of the detailed description which follows, taken together with the accompanying drawings wherein one embod iment of the invention is illustrated. It is to be expressly understood, however, that the drawings are for the purpose of illustration and description only, and are not designed as a definition of the limits of the invention.

In the drawings, wherein like reference characters refer to like parts throughout the several views,

Figure 1 is a diagrammatic illustrationof the rudder control system of the novel lightweight automatic pilot of the present invention Figure 2 is a view similar to that of Figure 1 illustrating the aileron and elevator control systems hereof; and,

Figure 3 is a detail view showing the motor control and clutch control electrical hook-up of the novel pilot hereof.

Referring now to the drawings and more particularly to Figure 1 thereof for a more detailed description of the present invention, the mechanism for actuating a rudder control surface 10 comprises a magnetic pick-up unit, generally designated with the reference character I I, which is constituted by three laminated legs or cores i2, i3 and It, each of which is provided with a single primary or energizing winding l5, l6 and H, the latter being connected in series with each other and with a secondary winding I8. of a transformer 19 whose primary winding 2015 connected with a suitable source of alternating current (not shown). Moreover, interposed between the primary or energizing windings is a battery 2| whereby windings l5, l6 and IT are fed with undulating or varying unidirectional current. The cores I2, is and I l, further are provided with secondary windings 22, 23 and 24 which are Y-connected at the inner ends and at their outer ends connect by way of leads 25, 26 and 21 with a three phase wound stator 28 of an inductive coupling device 29.

Although but one pic'z-ttp device H has been illustrated, two such devices may be used and interconnected together to thereby provide a greater working signal as shown in copending application Serial No. 624,710 filed October 26, 1945, now abandoned. The pick-up unit H is rigidly fastened directly to some part of the craft such as the wing, for example, where a minimum of disturbance due to local magnetic fields exists.

Assuming magnetic pick-up device H to be disposed in the earths magnetic field in a substantially horizontal plane (which is established by the gyro vertical pick-offs to be hereinafter more fully described) and with no energizing current in primary winding i5, i6 and H, the

fiux of the earths magnetic field will thread each s.

of the cores l2, I3 and i4 varying in amount with the angular disposition of each core relative to the field. So long as the earths fiux in each core or leg is in a steady state, no voltages will be induced in secondaries 22, 23 and 24 but as soon as undulating or a varying uni-directional current is supplied to primary windings IE, it and I1, the cores are saturated periodically, or once per cycle of the current at the source connected to primary of the transformer, whereby the earths fiux will leave cores l2, l3 and id at a rate depending upon the frequency of the current source. Voltages will be induced in secondary windings 22, 23 and 24 setting up therein as well as within wound stator 23 alternating currents having the s nte frequency as the fundamental frequency of the current source. Pick-up device I I thus operates as an earth inductor compass in that for every craft deviation from a prescribed course, however small, the induced voltages at secondaries 22, 23 and 24 will vary in accordance with and be proportional to the deviation.

For a condition of equilibrium, with the craft on course and in a substantially horizontal plane,

the voltages Within the stator windings 28 will correspond to the voltages at the three taps of secondaries 22, 28 and 24 of the pick-up device. At the same time, a rotor winding 32 inductively coupled with stator shaft 3| will be in an angular position with its electricalaxis llOlll" al to the res ltant of the magnetic field of the stator windings so that the voltages in the latter have no inductive effect on the rotor winding. As soon as the craft deviates from a prescribed course, the voltages at secondaries 22, 23 and 2e will vary causing a variation in the voltages of each of the stator windings. Such a change at the stator produces an angular change in the resultant of the magnetic field thereat and, since the electrical axis of the rotor winding is no longer normal to the resultant of the field at the stator, a signal is induced Within rotor winding 36 which is proportional to the angle of craft deviation from its prescribed course.

The signal induced within rotor winding 39 is fed by Way of conductors 32 into a conventional vacuum tube amplifier 2-3, the output of which is connected by leads 36 to the variable phase winding 35 Ma two phase induction motor 36, the

28 and carried by a suitable second phase winding 31 of which is continuously energized from a source of alternating current such as the source connected to the primary 20 of transformer l9. A conventional phase shifting network (not shown) may be provided in amplifier 32 so that the phases of the current within the tWo motor windings will be substantially apart.

Upon energization of phase winding- 35, the motor 36 drives rotor winding 36 directly through shaft 3i to a null position, i. e., a position wherein the electrical axis of the rotor winding assumes a position normal to the new resultant of the stator field at which point the signal in winding 39 approaches zero and phase winding 35 of the motor is de-energized whereupon the motor comes to a stop.

As will hereinafter more fully appear, motor 3E: is locked against rotation during automatic flight, so that a signal developed by pick-up device H as a result of a deviation from a prescribed course will be reproduced within rotor winding Si], and since the latter cannot be driven to a null by the motor, the signal thereof is communicated by leads 33 and 39 to the input of a conventional vacuum tube amplifier it and out therefrom by way of conductors ll to the variable phase 12 of a two phase servomotor 43, the second phase ti l of which is constantly energized from a suitable source of alternating current. Amplifier 58 may be of the character illustrated and described in the aforementioned copending application Serial No. 516,488.

Energization of variable phase 42 causes the servcmotor to drive rudder control surface I!) thro'gh an electromagnetic clutch t5 and a speed reduction gearing 46. Operation of motor 43 causes displacement of a rotor winding 41, which is connected to a suitable source of current, through a speed reduction gear system 28, the winding, being displaced relative to its stator winding it, whereby a signal is induced in the latter and fed by way of a lead 55! to be impressed on the direction signal at the input of amplifier 38. Stator i9 and rotor 21 constitute an inductive follow-up device developing a follow-up signal with can craft deviation.

By impressing upon the direction signal, another signal that is dependent upon the crafts angular velocity or rate of turn, it is possible to control craft oscillation whereby dead heat steering and extreme stability under all weather conditions can be obtained. To this end a rate of turn gyro is provided having a rotor 55 provided.

with normally horizontal Spill axis and supported byway of trunnions 52 within a gimbal frame 53, the frame being supported by outer trunnions 5 3 and 55 for oscillation about a second horizontal axis perpendicular to the spin axis. Gyro precession is yieldably constrained to a rate of turn frnction by way of springs 53 connected to trunnion In order to generate a signal proportional to the rate of craft turn, an inductive transmitter device 5'! is provided comprising a three phase wound stator 58, two phases of which are interconnected through a resistor 59, and a wound rotor 69 connected with a suitable source of current and inductively coupled with the stator. Rotor 68, further, is mounted on trunnion 55 for motion therewith. Stator 58 has a voltage generated in each of its windings proportional, respectively, to the angular position of each of the windings relative to rotor 63 and the signal resulting therefrom is communicated by lead 6|, which connects stator 58 in series with the stator of thefoll'ow-up signal generating device, to be impressed upon the direction and follow-up signals at the amplifier input. A resistor 62 interposed between a lead 63 and lead 6| is provided so that an initial setting of the amount of rate signal to be fed into the rudder channel may be predetermined.

In the foregoing manner, three signals, i. e., direction, rate and follow-back are mixed or added algebraically within amplifier 40 and act to control operation of servomotor 43. During an initial craft displacement from a prescribed course, the rate signal aids the direction signal and opposes the follow-back signal so that rudder is applied more rapidly than it would be by the direction signal alone and during a return to course the rate signal (the crafts angular velocity now being in an opposite direction) opposes the direction signal but adds with the follo'vv-bac'k signal so that the craft is prevented from overswinging from its prescribed course once it returns thereto. This action provides the rudder with a slight deflection in an opposite direction when it approaches on course so that it is braked to remain on such course. The static rudder position is therefore made to be algebraically proportional to the sum of the rate and direction signals.

Signals for the control of the craft about the bank and pitch axes are derived from take-offs associated with an artificial horizon gyro, generally designated in Figure 2 with the reference character 64, whereby magnetic pick-up device II is stabilized in attitude, i. e., maintained in a substantially horizontal plane. To this end, gyro 64 comprises a driven rotor having normally vertical spin axis and mounted within a rotor frame 66 which is supported by trunnions 61 for oscillation about a horizontal axis within a gimbal ring 68, the latter being mounted by way of an outer trunnion 69 for oscillation about a second horizontal axis perpendicular to the first axis. The gyro is so arranged that its outer trunnion 69 is parallel with the fore and aft axis of the craft to thereby define the bank axis while trunnions 6'! are parallel with the crafts transverse axis to thereby define the pitch axis.

For actuating aileron surfaces I to thereby control the craft about its longitudinal axis and thus also stabilize the magnetic pick-up device II in bank, an inductive transmitter device II is provided having a wound stator I2 and an in ductively coupled rotor winding 73 carried by trunnion 69 for angular motion therewith. The rotor winding is connected to a suitable source of current while two of the stator windings are interconnected by a resistor 14 which is center tapped by a lead '!5 connecting the stator with the input of the aileron channel of an amplifier "I6. For a no bank condition, the normal servomotor 80 to drive aileron control surfaces through an electromagnetic clutch 82 and a speed reduction gearing 83. Operation of motor causes displacement of a rotor winding 84, which is connected with a suitable source of cur rent, through a speed reduction gear system 84a, the winding being displaced relative to its wound stator 85 whereby a signal is induced in the latter and fed by way or a lead 86 to the input of amplifier IS, the wound stators 85 and I2 being connected in series with each other and the amplifier input. Wound stator 85 and rotor winding 84 constitute an inductive follow-up device which develops a follow-up signal with each craft deviation about its longitudinal axis, this signal being added algebraically to the bank signal for aileron control.

For the purpose of actuating elevator surfaces 87 to thereby control the craft about its transverse axis and thus also stabilize magnetic pickup device I I in pitch, an inductive transmitter device 88 is provided comprising a fixed wound stator 89, two windings of which are interconnected by a resistor 99, the latter being center tapped by a lead 9I which connects the stator with the input of a vacuum tube amplifier 92, and a rotor winding 93 inductively coupled with the stator and connected with a suitable source of current, the rotor winding being carried by trunnion 91 of vertical gyro 64. Normally the rotor winding assumes a position relative to its stator in which its electrical axis is normal to the stator and no signal is induced in the latter. With craft pitch, however, relative motion is developed between stator 89 and rotor 93 and a signal is induced in the stator proportional to craft climb or descent.

The signal so developed within stator 89 is amplified within amplifier 92 and supplied at the output thereof by leads 94 to the variable phase 95 of a two phase servomotor 96, the second phase 91 of which is continuously energized from a suitabie source of current.

Upon the energization of variable phase 95, motor 95 drives elevator control surfaces 81 through an electromagnetic clutch 98 and a speed reduction gearing 99. Operation of motor 96 causes displacement of a rotor winding I00,

which is connected with a suitable source of current, through a speed reduction gear system IN, the winding being displaced relative to its wound stator I02 whereby a signal is induced in the latter and fed by way of a conductor I03 to the input of amplifier 92, the wound stators 89 and I02 being connected in series with each other position of rotor winding 73 relative to its stator is such that its electrical axis is perpendicular to the stator windings and no signal is induced in the latter. Upon a craft bank, rotor winding I3 moves angularly with trunnion 69 relative to the stator windings to thereby induce a signal in the latter proportional to the amount of craft bank which is amplified within amplifier IS and supplied at the output thereof by leads "8 to energize the variable phase I9 of a two phase servomotor 30, the second phase 8| of which is continuously energized from a suitable source of current. I

Energi'zation of the variable phase I9 causes and the amplifier input. Wound stator I02 and rotor winding I00 constitute an inductive followup device which develops a follow-up signal with each craft deviation about its transverse axis, the signal being added algebraically to the bank signal for elevator control.

The system thus far described constitutes an all electric automatic steering system providing three axes of control, i. e., with a given course and attitude established manually a subsequent engagement of the system will automatically maintain the craft on that course and in that attitude. In order to provide the human pilot with a readily accessible control for throwing the craft into an automatic turn, rudder turn, aileron turn and elevator turn devices I04, I05 and I06 are provided, each constituting a potentiometer having a resistor I01, I08 and I09 and a wiper or contact arm IIO, III and II2, wiper arm IIO being connected in series by way of lead 63 with wound stator 58 of the rate inductive device, wound stator 49 of the inductive follow-back device and the input of amplifier iIl; wiper arm I I I being connected in series by way of a lead II3 with the wound stator 85 of the inductive bank follow-up device, wound stator I2 of the bank inductive transmitter device and the input of amplifier I6, while wiper arm I I2 is connected in series by way of lead II with the wound stator I02 of the inductive pitch followback device, wound stator 89 of the pitch inductive transmitter device and the input of amplifier 92.

Each potentiometer resistor I01, I08 and I99 is connected across a related secondary winding H5, H6 and III of transformers having primary windings H8, H9 and I energized from a suitable alternating current source. Normally, wiper contacts IIII, III and H2 are located at a central point on resistors I01, I88 and H39 so that no signals are transmitted by turn devices I04, Hi5 and I06 to their respective control channels.

As shown and described more fully in copending application Serial No. 644,799, filed-February l, 1946, all three wiper contacts IID, III and I I2 may be mounted on a common shaft and operated by a single turn knob so that manipulation of the latter will throw the craft into any degree of turn desired. By displacing wiper contacts IIII, III and IIZ relative to their resistors I01, Hi8 and I09, rudder, aileron and elevator signals are developed independently of the magnetic pick-up device I I, the rate of turn gyro and the pitch and bank take-offs of the gyro vertical to deflect rudder, aileron and elevator surfaces to direct the craft into the degree of turn called for by the setting of the turn knob. In the aileron and elevator channels; the signals introduced by the displacement of wiper contacts III and H2 relative to their resistors deflect the aileron and elevator surfaces until the desired craft pitch and bank are attained whereupon, resulting from the craft attitude change, signals are developed by the bank and pitch take-offs II and 88 which will wash out the signals set in by movement of wiper contacts III and H2 when the craft attitude set in by the turn knob has been attained. Subsequent deviation from the required craft attitude is under the control of the gyro bank and pitch take-oifs.

Inasmuch as up-elevator is required in the event of either a left or right turn, the pitch turn device I06 differs from the rudder and aileron turn devices I04 and I85 in that secondary winding III of the former is connected at one end by way of a lead I2I with the opposite end of resistor I09 while the opposite end of secondary winding III is connected with the center of resistor I09 by way of a lead I22. By reason of such an arrangement, motion of wiper contact H2 in either direction from its central point on resistor I09 will provide a signal in one direction only, i. e., an up-elevator signal, as distinguished from the reversing signal introduced by wiper contact III by its movement from one side of its central position to the other side on resistor I08, for example.

During an automatic turn it is necessary to efiectively disconnect the magnetic pick-up device II from the rudder channel or otherwise any attempted craft turn would be nullified by device II, the latter acting to maintain the craft on its previously prescribed course. To this end, motor 36 which normally drives the rotor 30 of the inductive coupling device 29 to its null position is provided with an electromagnetic brake in the form of a plunger I23 which is maintained by a spring I24 out of engagement with the rotor of the motor. The plunger is inductively associated with a, coil I25 which connects through leads I26, a turn switch I27, leads I28 and a clutch switch I29 with a battery I30. Also connected, as better shown in Figure 3, for energization by the closure of clutch switch I29 are coils I3I, I32 and I33 for engaging clutches 45, 82 and 98 whereby rudder servomotor 43 is drivably engaged with rudder surface III, aileron servomotor is drivably engaged with aileron surfaces 10 and elevator servomotor 96 is drivably engaged with elevator surfaces 81.

During straight automatic flight, clutch switch I29 is closed to thereby establish a drivable connection between the servomotors and their related control surfaces and turn switch I21 is likewise closed thereby energizing coil I25 so that plunger I23 brakes the rotor of motor 36 against rotation so that any craft deviation in azimuth develops a signal in rotor winding 30 by the operation of the magnetic pick-up device II which acts to operate servomotor G3 and thereby actuate rudder surface II).

With the initiation of an automatic craft turn, i. e., when wiper contacts IIIl, III and H2 are displaced relative to their resistors I01, I08 and W9, turn switch I2'I is opened to de-energize coil I25 whereupon spring I24 retracts plunger I23 from engagement with motor 35 so that the latter is free to rotate in response to signals developed within rotor winding 30. Thus, during an automatic turn, even though magnetic pickup device II is constantly developing a signal proportional to the amount of craft displacement in azimuth which signal is reproduced within rotor winding til, the motor 35 being free to turn drives rotor 30 to its null so that no displacement signal is available from pick-up device II for the rudder channel during such a turn.

By providing an arrangement whereby motor 36 is locked against rotation during straight automatic flight and is unlocked for rotation and operation during manual flight or during an automatic craft turn, a novel synchronization feature is presented whereby the system is always in synchronism, i. e., prior to the initiation of straight automatic flight the rotor winding 30 of the coupling inductive device is at its null position to immediately take over control of the rudder surface. In response to any deviation from a prescribed course a signal is developed within winding 39 proportional to the deviation and since motor 36 is braked or locked and cannot drive winding 30 to its null, the signal is communicated from winding 30 to operate servomotor 43? During straight automatic flight, switches I21 and I29 are closed but during an automatic turn switch I2? is opened to free motor 36 for operation. During manual flight, on the other hand, clutch switch I29 is opened to disconnect the servos and permit manual control of the surfaces. At such time, even though turn switch I21 is closed, coil I25 is de-energized, since it connects with battery 30 through the clutch switch, to thereby release motor 36 for operation.

Even though the rudder channel has been shown as provided with an amplifier II] and aileron and elevator channels withseparate amplifiers I6 and 92, it is to be understood that but one amplifier is needed containing all three channels as shown in the aforementioned copending application Serial No. 516,488.

Under certain conditions it is desired to trim rudder and/or aileron and elevator and to this end novel rudder trim, aileron trim and elevator trim devices I35, I36 and I3! are provided. Rudder trim device I35 comprises a potentiometer having a resistor I38 connected across a secondary winding I39 of the transformer having winding II 8 for its primary. A central tap of the secondary winding is grounded by way of a conductor I40 while resistor I38 is provided with a wiper contact I4I which is arranged at a normally central point on resistor I38, wiper MI being connected by way of a lead I42 with a central portion of secondary winding I I5. Thus arranged, rudder trim device I35 is in series with rudder turn device I04, the rate inductive device, rudder inductive follow-back device and the input of the rudder channel of the amplifier.

Aileron trim device I36 comprises a potentiometer having a resistor I44 connected across a secondary winding I45 of the transformer having winding I I 9 for its primary. A central tap of the secondary winding is grounded by way of a conductor I 4'! while resistor I44 is provided with a wiper contact I 48 which is arranged at a normally central point on resstor I44, wiper I48 being connected by way of a lead I49 with a central portion of secondary winding II6. As will be apparent, aileron trim device I33 is in series with aileron turn device I05, stator 85 of the bank follow-back device, stator I2 of the bank take-off de ice and the input of the aileron channel of the amplifier.

Elevator trim device I31, on the other hand, comprises a potentiometer having a resistor I50 connected across a secondary winding I I of the transformer having winding I20 for its primary. A center tap of the secondary winding is grounded by wav of a conductor I52 while resistor I50 is provided with a wiper contact I53 which is arranged at a normally central point on resistor I50, wiper I53 being connected by way of a lead I54 with secondary winding I IT at that end which connects by way of lead I22 with the center tap of resistor I09 of the pitch turn device I05. Thus arranged, elevator trim device I31 is in series with elevator turn device I 03, stator I04 of the pitch follow-back device, stator 89 of the gyro pitch take-off device and the input of the elevator channel of the amplifier.

If left or right rudder trim is required, wiper arm MI is displaced relative to resistor I38, above or below the center point thereof, and the required signal is fed by lead I42 into the rudder channel of the am lifier. Similarly for bank or pitch trim, wiper contacts I48 and I53 are displaced relative to their resistors I44 and I50, above or below their normally central position, to feed required bank or pitch trim signals in the aileron and/or pitch channel of the amplifier.

There has thus been provid d a novel and simple as well as lightweight pilot for small and fast craft having novel means therein whereby the system is always synchronized for taking immediate and smooth control of the craft in azimuth whether subsequent to manual flight or to an automatic turn. In all other respects the general operation of the system is similar to that described in copending application Serial No. 516,439, filed Defember 31, 1943.

Although but a single embodiment of the invention has been illustrated and described in detail for controlling a craft about one or more axes thereof, it is to be expressly understood that the invention is not limited thereto. Various changes may also be made in the design and arrangement of the parts without departing from the spirit and scope of the invention as the same will now be understood by those skilled in the art. For a definition of the limits of the present invention reference will be had primarily to the appended claims.

What is claimed is:

1. In an automatic steering system for an aircraft having a rudder surface and driving means for operating the rudder surface, the combination of an inductive device having a multi-polar stator winding and a rotor winding, an actuating device connectd to said rotor winding for driving the latter relative to said stator winding, a soune Or" current, direction responsive means including an induction device comprising a core of permeable magnetic material adapted to receive a magnetic flux from a unidirectional magnetic field, a multi-polar stator winding on said core, a single phase winding on said core conn cted for energization by said source of current, means for interconnecting the multi-polar winding of said core to the multi-polar winding of said indutive device whereby a signal proportional to a relative angular disp'acement of said direction responsive means in azimuth is developed within said rotor winding. means connesting th rudder driving means with said rotor windinr, means electrically connecting said rotor winding to said actuating device for energizing the latter to drive said rotor winding to a null position at which time no signal is available for the rudder driving m ans, and means for braking said actuating device against operation whereby the signal developed within said rotor winding is communicated to the rudder driving means.

2. In an automatic steering system for an aircraft having a rudder surface and driving means for operating the rudder surface, the combination of an inductive device having a multi-polar stator winding and a rotor winding, a servomotor connected to said rotor winding for driving the latter relative to said stator winding, a source of current, direction responsive means including an induction device comprising a core of permeable magnetic material adapted to receive a magnetic flux from a unidirectional magnetic field, a multi-polar stator winding on said core, a single phase winding on said core connected for energization by said source of current, means for interconnocting the multi-polar winding of said core to the multi-polar winding of said in ductive device whereby a signal proportional to a relative angular displacement of said direction responsive means in azimuth is developed within said rotor winding, means connecting the rudder driving means with said rotor winding, means electrically connecting said rotor Winding to said servomotor for energizing the latter to drive said rotor winding to a null position at which time no signal is available for the rudder driving means and the rudder surface and the direction responsive means are thus maintained in synchronisin, and means for braking said servomotor against operation whereby the signal developed within said rotor winding is communicated to the rudder driving means.

3. In an automatic pilot for aircraft provided with a rudder surface, the combination of course change responsive means for normally controlling 11 the rudder surface to maintain the craft against deviation from a prescribed course during linear flight, rudder turn means for developing a signal to actuate the rudder surface and thereby change the craft course independently of said course change responsive means, means for operating said rudder turn means, means for making the course change responsive means ineffective on said rudder, and rudder trim means connected in series with said rudder turn means for trimming the rudder surface.

4. In an automatic pilot for aircraft provided with a rudder surface, the combination of course change responsive means for normally controlling the rudder surface to maintain the craft against deviation from a prescribed course during linear flight, rudder turn means comprising a normally balanced potentiometer device for developing, when unbalanced, a signal to actuate the rudder surface and thereby change the craft course independently of said change responsive means, means for unbalancing said potentiometer device, and means for making the course change responsive means infiective on said rudder.

5. In an automatic pilot for aircraft provided with a rudder surface, the combination of course change responsive means for normally controlling the rudder surface to maintain the craft against deviation from a prescribed course during linear flight, rudder trim means comprising a normally balanced potentiometer device for developing, when unbalanced, a rudder trim signal, means for unbalancing said potentiometer device, rudder turn means comprising a normally balanced potentiometer device connected in series with said rudder trim means for developing, when unbalanced, a signal to actuate the rudder surface and thereby change the craft course independently of said change responsive means, means for unbalancing said rudder turn potentiometer device, and means for making the course change responsive means ineffective on said rudder.

6. In an automatic pilot for aircraft provided with a rudder surface, the combination of course change responsive means for normally controlling the rudder surface to maintain the craft against deviation from a prescribed course during linear flight, rate of course change responsive means for modifying operation of the rudder surface, rudder turn means connected in series with said rate of course change responsive means for developing a signal to actuate the rudder surface and thereby change the craft course, means for actuating said rudder turn means, and means for making the course change responsive means ineffective on said rudder.

'7. In an automatic pilot for aircraft provided with a rudder surface, the combination of course change responsive means for normally controlling the rudder surface to maintain the craft against deviation from a prescribed course during linear flight, rudder trim means for developing a signal in addition to the control of said course change responsive means to trim the rudder surface, means for actuating said rudder trim means, rudder turn means connected in series with said rudder trim means for developing a signal to actuate the rudder surface and thereby change the craft course independently of said course change responsive means, means for actuating said rudder turn means, and means for making the course change responsive means ineffective on said rudder.

8. In an automatic steering system for mobile craft having a control surface and driving means for operating the surface, the combination of reference means for producing a signal in response to a departure of said craft from a predetermined position to energize the driving means, means connected for operation by the driving means for producing a second signal for modifying the energization of the driving means, turn means connected in series with said second signal producing means for altering craft position comprising a normally balanced potentiometer device having a wiper arm at a central point thereof for developing a third signal to energize the driving means and thereby turn the craft in a preselected manner, and means operable during operation of said turn means for making said reference means ineffective on said driving means.

9. An automatic pilot for positioning a control surface of a craft comprising an earth inductor device adapted to provide a signal voltage output varying with changes in relative position of the inductor device and the earths magnetic field, a signal transformer having a stator winding connected to receive the output of the inductor device and a rotor including a winding associated therewith, means connected to receive the signal voltage induced in said rotor winding and controlled w. in

thereby for controlling the position of said rotor relative to said stator whereby to zero the signal voltage induced in said rotor winding, a servomotor for actuating said control surface, means responsive to the signal of said rotor winding for actuating said servomotor, and means operable during straight craft flight for making said positioning means ineffective on said rotor winding.

10. An automatic pilot for positioning a control surface of a craft comprising an earth inductor device adapted to provide a signal voltage output varying with changes in relative position of the inductor device and the earths magnetic'field, a signal transformer having a stator winding connected to receive the output of the inductor device and a rotor including a winding associated therewith, means connected to receive the signal '"voltage induced in said rotor winding and controlled thereby for controlling the position of said rotor relative to said stator whereby to zero the signal voltage induced in said rotor winding, a servomotor for actuating said control surface, means responsive to the signal of said rotor winding for actuating said servomotor, means operable during straight craft flight for making said positioning means ineffective on said rotor winding, turn means for actuating said servomotor to alter craft course, and means for making said rotor positioning means effective on said rotor winding.

11. An automatic pilot for positioning a control surface of a craft comprising an earth inductor device adapted to provide a signal voltage output varying with changes in relative position of the inductor device and the earths magnetic field, a signal transformer having a stator winding connected to receive the output of the inductor device and a rotor including a winding associated therewith, means connected to receive the signal voltage induced in said rotor winding and controlled thereby for controlling the position of said rotor relative to said stator whereby to zero the signal voltage induced in said rotor winding, a servomotor for actuating said control surface, means responsive to the signal of said rotor winding for actuating said servomotor, and means for making said rotor positioning means effective and ineffective on said rotor Winding.

12. In an automatic steering system for an aircraft havin a positioning surface and driving means for operating the surface, the combination of an inductive device having a multipolar stator winding and a rotor winding, an actuating device connected to said rotor winding for driving the latter relative to said stator Winding, a source of current, direction responsive means including an induction device comprising a core of permeable magnetic material adapted to receive a magnetic flux from a unidirectionaI magnetic field, a multi-polar stator winding on said core, a single phase winding on said core connected for energization by said source of current, means for interconnecting the multi-polar winding of said core to the multipolar winding of said inductive device whereby a signal proportional to a relative angular displacement of said direction responsive means in azimuth is developed within said rotor winding, means connecting the surface driving means with said rotor winding, means electrically connecting said rotor winding to said actuating device for energizing the latter to drive said rotor winding to a null position at which time no signal is available for the surface drivin means, and means for making the actuating device inefiective on said rotor winding whereby the signal or the latter is communicated to said surface driving means.

13. In an automatic pilot for positioning a control surface of a craft, reference means for positioning said surface comprising a two-part signal generator for providin a signal voltage output varying with changes in craft position relative to a preselected position, one part of said signal generator being fixed to said craft and the other part thereof being movable rela- 14 tive to said fixed part, turn means for producing a signal to assume primary control of said surface, and means adapted for operation when said surface is under the control of said turn means for driving the movable part of said signal generator to a non-signal generating position relative to said fixed part.

ALAN M. MACCALLUM.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,958,258 Alexanderson May 8, 1934 2,005,530 Boykow June 18, 1935 2,126,855 Wunsch et al Aug. 16, 1938 2,159,142 Fischer May 23, 1939 2,183,932 Carlson Dec. 19, 1939 2,190,390 Thiry Feb. 13, 1940 2,196,385 De Florez et a1. Apr. 9, 1940 2,256,875 Wade Sept. 23, 1941 2,270,875 Hanson et a1 Jan. 27, 1942 2,361,790 Noxon Oct. 31, 1944 2,398,421 Frische et a1 Apr. 16, 1946 2,416,097 Hansen et a1 Feb. 18, 1947 2,429,642 Newton Oct. 28, 1947 2,450,084 Emerson Sept. 28, 1948 2,452,311 Markusen Oct. 26, 1948 2,464,629 Young Mar. 15, 1949 OTHER REFERENCES Electronics, of October, 1944, pages 110-117, inclusive. 

